This invention relates to apparatus for the formation of metal powders which are cooled at high rates, and more particularly to the use of an atomizer rotor, or cup, for receiving molten metal and flinging it radially outwardly from the rotor as liquid metal droplets. Specific apparatus for using an atomizer rotor, or cup, as disclosed in this application, is shown in U.S. Pat. Nos. 4,025,249 and 4,053,264. A further disclosure of an apparatus and method for using such a rotor cup is set forth in application Ser. No. 654,247 now abandoned and application Ser. No. 751,004, now U.S. Pat. No. 4,078,873. Other prior art patents showing various types of cups are listed below: U.S. Pat. No. 2,062,093; U.S. Pat. No. 2,310,590; U.S. Pat. No. 2,439,772; U.S. Pat. No. 2,439,776; U.S. Pat. No. 2,699,576; U.S. Pat. No. 3,196,192; and U.S. Pat. No. 3,329,746. It is noted that the atomizing cup can be used with many different types of apparatus and in different methods for producing metal powder.